#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
#define rep(i, a, b) for (int i = (a); i <= (b); i++)
#define per(i, a, b) for (int i = (a); i >= (b); i--)
#define endl '\n'
const int N = 2e5 + 5;

int n, m;
int a[N];
ll solve(ll x, ll y) {
  ll z = x & y;
  if (!z) return 0;
  // find the most significant 1
  per(i, 63, 0) {
    ll a = 1ll << i;
    if (!(a & z)) continue;
    ll mask = a - 1;
    ll b = max(x & mask, y & mask);
    ll c = a - b;
    return c + solve(x + c, y + c);
  }
  return -1;
}
int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  int t;
  cin >> t;
  while (t--) {
    ll x, y;
    cin >> x >> y;
    if (x == y)
      cout << -1 << endl;
    else
      cout << solve(x, y) << endl;
  }
  return 0;
}